Method of Upgrading a Heavy Oil Feedstock

ABSTRACT

A pretreatment process is described for heavy hydrocarbon oil feedstock, such as oils extracted from tar sands. The feedstock is passed through a heated, continuous flow electron or x-ray treatment zone. The process is designed to allow the feedstock to be conditioned with ozone-containing air, steam or a hydrogen donor gas prior to electron/x-ray treatment. The ozone-containing air stream may be the stream produced in the electron treatment zone. After conditioning, the heavy oil is heated to a specified temperature and uniformly treated with high-energy beams of electrons or x-rays. A key feature of the invention is the electron/x-ray treatment zone may use multiple accelerators or a beam splitter to ensure acceptable dose distributions in the flowing feedstock. Another key feature is the recirculation of volatiles back into the feedstock. According to the novel feature, the process produces a treated feedstock having a lower average molecular weight and boiling point than the original feedstock, without significant coke formation. The fraction of gas oil collected during distillation is increased significantly.

This application claims the benefit under 35 U.S.C. 119(e) of U.S. provisional application Ser. No. 60/812,099, filed Jun. 9, 2006.

FIELD OF THE INVENTION

This invention relates to the upgrading of a heavy oil feedstock, for example bitumen extracted from tar sands. This pretreatment process can be tailored for the specific hydrocarbon mixture used and the final upgraded oil properties desired. The process variables include electron dose, dose rate, temperature during electron treatment, pressure and selective additives to enhance the electron effect.

BACKGROUND

Heavy oil and bitumen consist of large hydrocarbon molecules. Upgrading processes add hydrogen atoms and/or remove carbon atoms, which converts the bitumen into a product similar to conventional light crude oil.

The direct upgrading of heavy crude oils is difficult. Distillation typically yields low levels of distillates. The remaining residual oils cannot be added in significant amounts to fluid catalytic crackers because of the extraordinarily high levels of metals and carbon residue, which result in a high level of hydrogen generation and high coke on catalyst respectively. Therefore, coking, which is one of several thermal cracking processes, has traditionally been the process of choice for upgrading heavy oils. While coking does remove a significant amount of the metals and carbon residue, the quality of the produced liquids is poor. They are high in sulfur, olefins, diolefins and heavy aromatics and, as a result, require a substantial amount of additional hydrotreating.

One alternative to coking is visbreaking, which is another widely applied thermal cracking process for the conversion of residual oils (J. F. LePage et al.; Resid and Heavy Oil Processing, Editions Technip, Paris, France, 1992). Thermal visbreaking is characterized by high temperature and short residence time; so that, unlike coking, the cracking reactions are terminated before coke is made. Visbreaking alone does not significantly change the heteroatom content (S, N), metals or asphaltene content of the feed. Its sole function is molecular weight (e.g. boiling range) reduction and, hence, lowering of viscosity.

An issue with thermal visbreaking is that visbreaking and other mild thermal processes result in cleavage of the alkyl side chains from asphaltenes, resulting in the asphaltenes precipitating and subsequently forming deposits, which, if not controlled, foul processing equipment with coke. (R. C. Schucker and C. F. Keweshan, The Reactivity of Cold Lake Asphaltenes, Prepr. Div. Fuel Chem., Amer. Chem. Soc., 1980, 25(3), 155-165). Solvent extraction of the asphaltenes is possible, but results in high energy consumption for solvent removal and larger equipment sizes. Therefore, there remains a need in the art for improvements to heavy feed upgrading that will overcome the above shortcomings.

The process of radiation-thermal cracking (RTC) and its individual fractions was investigated by Soviet scientists and these data are presented in the following documents:

Method for Oils and Oil Residua Refining, Patent of Republic of Kazakstan N 4676 of 16 Jul. 1996 (Priority of Kazakstan N 940434.1 of 14 Apr. 1994).

Zaykin Y. A., Zaykina R. F., Nadirov N. K., Mirkin G. System for Complex Natural and Industrial Chemical Compounds Reprocessing and Regeneration. Priority of Kazakstan 970592.1 of 26 Jul. 97.

Chesnokov B. P., Nadirov N. K., Kiryshatov O. A., Kiryshatov A. I., Zaykin Y. A., Zaykina R. F., Vaytsul A. N. Method for Chemical Reactions Initiations During Oil and Oil Products Processing and Device for Its Realization. Priority of Russia N 97-10-7263/25 (007710).

Mirkin G., Nadirov N. K., Zaikina R. F., Zaikin Y. A. System for processing and refining chemical compositions. Priority of U.S.A N 09/100, 453 of 06/19.

Other related references include:

Reference 1: G. M. Panchenko, A. V. Putilov, T. N. Zhuravlov et al. Investigations of the basic rule of the radiation thermal cracking of N-hexadecane. High Energy Chemistry, v. 15, #5, 1981, p. 426

In Reference 1, the process was demonstrated with n-hexane. The gamma dose rate changed from 7.8 up to 16.7 Gy/s, the maximally absorbed dose constituted 20 kGy. The autoclave pressure depended on temperature and conditions of the experiment and did not exceed 10 MPa. The experiments were conducted at temperatures from 300 to 400° C. The experimental conclusions included the possibility of using a high-temperature nuclear reactor to irradiate production volumes of heavy oil.

Reference 2: G. I. Zhuravlov, S. V. Voznesenskiy, I. V. Borisenko et al. Radiation-thermal effect on the heavy oil residium, High Energy Chemistry, v. 25, #1, 1991, p. 27.

According to Reference 2 gas oil was subjected to radiation thermal cracking at temperatures of 300° to 400° C. in the dose range 50 to 200 kGy, with a gamma dose rate of 5.1 Gy/s. This study showed that the low dose rate RTC process increased the conversion of molecular weight compounds by 50 to 100% as compared to the thermal process alone. Irradiation also contributed to the process of sulphur removal of the light oil products obtained. As in Reference 1, the authors described an industrial process of applying heat and radiation from a nuclear reactor.

Reference 3: N. K. Nadirov, R. F. Zaykina, Yu. A. Zaykin. State and perspectives of radiation treatment of heavy oil and natural bitumen. NIIETF KazGY, NPO “Kazneftebitum”, Alma-Ata, Kazakhstan (1995).

Reference 3 presented the results of a study of RTC of a mixture of heavy oil fractions with boiling point of greater than 400° C., using a 4 MeV linear accelerator. The dose rate was varied from 1 to 4 kGy/s, with an absorbed dose of 1 to 40 kGy. Both static and flowing experiments were completed. Under these irradiation conditions, the optimal temperature for the RTC process was 400 to 420° C. The output of gasoline fractions with a boiling temperature of less than 200° C. was 50% higher than that for thermal cracking alone. The gasoline fraction obtained had a high octane range (76 to 80) and low sulfur content. The percentage of aromatic and naphthenes compounds also increased with the RTC process than with thermal cracking alone.

Reference 4: Wu G., Katsumura Y., et al. Effect of radiation on the thermal cracking of n-hexadecane, Ind. And Eng. Chem. Res.—1997, 36, N6, p. 1973

Reference 4 describes liquid and gas-phase RTC cracking of n-hexane at 300 to 400° C., with gamma irradiation. The liquid phase was irradiated with dose rates ranging from 150 to 460 Gy/h and the gas phase was irradiated with dose rates ranging from 240 to 560 Gy/h. It was shown that irradiation abruptly increased the process rate, not affecting the set of final carboniferous cracking products. A large amount of molecular hydrogen was formed by radiation thermal cracking.

Reference 5: A. K. Pikaev. New elaboration of radiation technology in Russia (review). High Energy Chemistry, v.33, #1, 1999, p. 3

Reference 5 describes development work to commercialize RTC using gamma irradiation in a closed static system. The volume of the test vessel was 120 cm³. The results obtained from this higher volume experiment corresponded to literature data in the temperature range of 250 to 300° C. The volume of light gas fractions was increased by up to 5%, with a lowering of viscosity of the remaining oil. A large amount of hydrogen, saturated and unsaturated hydrocarbons, and hydrogen sulphide were also identified in the reaction vessel.

Reference 6: R. F. Zaykina, Yu. A. Zaykin, T. B. Mamonova, and N. K. Nadirov, Radiation-thermal processing of high-viscous oil from Karazhanbas field, Rad. Phys. Chem., 60 (2001) 211-221.

Reference 6 examined the RTC process for high-viscous oil from Karazhanbas, using electron beam (EB) treatment from a 2 MeV, 4 kW linear accelerator. The unique feature of their experimental set-up was that the oils were heated from 200° C. to 400° C. by continuous EB treatment, and the volatiles were removed from the oil during irradiation. The study confirmed that total dose and dose rate impact both the yield and the composition of the gas oil fractions with boiling temperatures up to 350° C. The mechanisms associated with the formation of aromatic hydrocarbons were also discussed.

Reference 7: Yu. A. Zaykin and R. F. Zaykina, Simulation of radiation-thermal cracking of oil products by reactive ozone-containing mixtures, Rad. Phys. Chem, 71 (2004) 475-478.

Reference 7 described the benefits of combining RTC and ozonolysis to lower the temperature required to maximize the gas oil fractions with boiling points below 350° C. The RTC process required a preheating temperature of 420° C., while bubbling ozone-containing air through the oil lowers the required treatment temperature by 15 to 20° C. This combined process was shown to reduce the concentration of high-molecular weight aromatic compounds as well.

Reference 8: R. F. Zaykina, Yu. A. Zaykin, Sh. G. Yagudin and I. M. Fahruddinov, Specific approaches to radiation processing of high-sulfuric oil, Rad. Phys. Chem., 71 (2004) 467-470.

Reference 8, a follow-on to Reference 7, describes the beneficial effects of the RTC/ozonolysis process for the desuphurization of light fractions of gas oil and considerably reduced the total amount of sulphur concentrated in high-molecular weight compounds.

A typical process for upgrading hydrocarbon feedstock is the thermal cracking process. Illustratively, process fired heaters are used to provide the requisite heat for the reaction. The feedstock flows through a plurality of coils within the fired heater, the coils being arranged in a manner that maximizes the heat transfer to the hydrocarbon flowing through the coils. In conventional coil pyrolysis, dilution steam is used to inhibit coke formation in the cracking coil. A further benefit of high steam dilution is the inhibition of the coke deposition in the exchangers used to rapidly quench the cracking reaction. An illustration of the conventional process is seen in U.S. Pat. No. 3,487,121 (Hallee).

The use of steam in the hydrocarbon stream requires larger furnace capacity and equipment than would be necessary for the hydrocarbon without steam. Further, when steam is used, energy and equipment must be provided to generate and superheat the steam.

A variety of attempts have been made to pretreat heavy hydrocarbon feedstock to render it suitable for thermal cracking. An option is the vaporization of the feedstock with large quantities of steam to create a very low system partial pressure (Gartside, U.S. Pat. No. 4,264,432). Others have proposed solvent extraction pretreatment of the hydrocarbon to remove the asphaltene and coke precursors. Another attempt is the thermal pretreatment of resids to yield a heavy hydrocarbon, then catalytically hydrotreating a portion of the heavy hydrocarbon feedstock before the steam cracking step (U.S. Pat. No. 4,065,379, Soonawala, et al.) and similarly, the pre-treatment of hydrocarbon feedstock by initial catalytic cracking to produce a naphtha or naphtha-like feed for ultimate thermal cracking (U.S. Pat. No. 3,862,898, Boyd, et al.). These processes all improve the cracking of heavy hydrocarbon, however, in most instances the process suffers from either the expense of large steam dilution equipment or the unsatisfactory increase of tar and coke accumulation in the process equipment.

Known attempts to upgrade a heavy oil feedstock have thus far yielded unsatisfactory results.

SUMMARY

According to one aspect of the invention there is provided a method of upgrading a heavy oil feedstock, the method comprising:

forming a continuous flow of the heavy oil feedstock;

heating the continuous flow to a prescribed temperature;

cracking the heavy oil feedstock in the continuous flow by directing electrons or x-rays at the continuous flow.

The method may include recycling a separated portion comprising volatized parts back into the continuous flow prior to electron and/or x-ray cracking.

Constituents of the continuous flow subsequent to electron/x-ray cracking can be varied by varying an amount of the separated portion recycled back into the continuous flow.

A separated portion, comprising parts of the continuous flow which are volatized when heating the flow to said prescribed temperature, are preferably recycled back into the flow.

Conditioning the continuous flow prior to electron/x-ray treatment, may include adding to the flow a selected one or more of ozone, steam, a hydrogen donor gas, or recycling back into the flow a portion of the continuous flow which is volatized when preconditioning.

Electron/x-ray cracking is preferably done at or near atmospheric pressure.

The continuous flow may be mixed during electron/x-ray cracking by providing baffles in a path of the flow or by providing moving mixing blades in a path of the flow.

The electrons or x-rays are directed at the continuous flow from a plurality of opposing directions.

As described herein a continuous flow process for the upgrading of a heavy oil feedstock may comprise the steps of preheating the feedstock, electron or x-ray cracking said feedstock, using electron beams from an accelerator, at conditions that will produce a cracked product stream having a lower average molecular weight and boiling point than said feedstock without significant coke formation; collecting from said product stream light ends that volatilize, including any water that might be in the stream; and feeding both the volatized product stream and the heated liquid product stream to the heavy oil distillation process.

The feed may comprise a heavy oil stream having an API gravity of less than 20°.

The electron accelerator may be either a pulsed or continuous beam design, with a beam power ranging from 1 to 700 kW and a beam energy ranging from 1 to 12 MeV.

The electron/x-ray treatment zone may be vented, with the volatized gas stream being sent to the distillation process directly or circulated through the feedstock preheating tank prior to being sent to the distillation process.

Air may be circulated through the feedstock storage tank to incorporate ozone into the feedstock. Ozone is produced during the electron treatment of air.

The pretreatment system may introduce steam or a hydrogen donor gas, or both, to the feedstock either prior to heating or just before electron or x-ray treatment.

The method may further include arranging a portion of the continuous flow to comprise hydrocarbons having a boiling point lower than said prescribed temperature prior to electron or x-ray cracking by maintaining under pressure in the continuous flow at least a portion of hydrocarbons volatized during heating.

One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic illustration of a preferred embodiment of the method of upgrading a heavy oil feedstock according to the present invention.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

The present invention relates to a process for upgrading petroleum feedstocks, using a combination of electron cracking, with and without added ozone, steam or hydrogen, at conditions that will not produce significant amounts of coke. Suitable feedstocks for use in the present invention include heavy and reduced petroleum crude oil; petroleum atmospheric distillation bottoms; petroleum vacuum distillation bottoms, or residuum; pitch; asphalt and tar sand bitumen. Such feeds will typically have a Conradson carbon content of at least 5 wt. %, generally from about 5 to 50 wt. %. As to Conradson carbon residue, see ASTM Test D189-165.

Electron cracking, as employed herein, usually results in about 15 to 70 wt. % conversion of the heavy oil feed to lower boiling products (boiling temperature <350° C.). This conversion rate is typically 50% to 100% higher than using the current thermal cracking process. The entire group of reactions takes place in the “electron treatment zone”; and the average residence time of the feed in the treatment zone is a function of the power of the machine being used and the design of the flow chamber. The residence time has to be sufficient to allow the feed stream to absorb 1 to 50 kJ of electrons per kilogram of feedstock, depending on the composition of the initial feed.

Our process is typically carried out at or near atmospheric pressure; however, some improvement in the quality and stability of the product can be achieved by the introduction of a hydrogen donor gas and/or steam.

Referring now to the overall process shown in FIG. 1, the feedstock is first formed into a continuous flow through a first flow line #1 prior to entering the inlet of a pre-heater (20) in series with the first flow line and which preheats the feedstock to a prescribed temperature. The flow exits an outlet of the pre-heater (20) at a second flow line #2 to be directed into an inlet of an electron treatment zone (22) in series with the second flow line #2. Within this zone (22), the flow is subjected to electrons generated from an electron accelerator facility (24). After treatment the flow exits an outlet of the zone (22) through a third flow line #6 which directs the flow to a first inlet of a distillation unit (26) where the various fractions of hydrocarbons in the flow are separated and passed onto subsequent refining operations.

Turning now more particularly to the flow at the first flow line 1, prior to entering the pre-heater (20), the feedstock may be preconditioned by the addition of steam and a hydrogen donor gas injected into either into flow line #1 prior to entering the pre-heater (20) or into flow line #2 between the pre-heater (20) and the electron treatment zone (22).

The pre-heater (20) in the illustrated embodiment is operated at low pressure such that any parts of the flow which are volatized due to the preheating can be vented from an auxiliary outlet of the pre-heater (20) through a vent line #3 to a control valve (28) in series with the vent line #3. The control valve then determines whether the vented volatiles are fed directly to the distillation unit (26) at an auxiliary inlet of the distillation unit separate from flow line #6 or alternatively fed through an additional flow line #4 for injection back into the continuous flow at flow line #2 just prior to entering the electron treatment zone (22).

Similarly the electron treatment zone (22) may also be vented from an auxiliary outlet at vent line #5 to remove any parts which are volatized during the electron treatment. A control valve #30 in series with the vent line #5 receives the volatiles vented from the electron treatment zone and then subsequently controls whether these volatiles are either directed back into the continuous flow at flow line #2 just prior to entering the electron treatment zone, or alternatively directed to the distillation unit (26) along with the volatiles vented from the pre-heater through vent line #3.

The electrons may be directed at the flow from multiple directions to ensure that substantially the entirety of the flow is subjected to electron beams.

When pre-treating or pre-conditioning the feedstock prior to entering the pre-heater (20), a conditioning tank may be provided in series with the flow line 1 of the flow prior to entering the pre-heater. The pre-treatment or pre-conditioning may comprise the addition of one or more of ozone, steam or a hydrogen donor gas as noted above.

According to the method described herein, the heavy oil feedstock is first formed as a continuous flow which is heated to a prescribed treatment temperature prior to the electron treatment zone (22). Heating may occur at the pre-heater (20) or both at a pre-heater and pre-conditioning stage prior to the treatment zone (22). When heating, parts of the flow having a boiling point lower than the prescribed treatment temperature will be volatized, but according to the present invention these volatized parts may be arranged to be present in the continuous flow prior to the electron treatment zone. This is accomplished either by maintaining the volatiles under pressure in the flow or by returning the volatiles to the flow just prior to the electron treatment zone. These hydrocarbons of lower molecular weight encourage a greater number of reactions and a greater degree of cracking of heavier oil molecules in the flow.

When it is desirable to vary the composition of molecules in the end product at the distillation unit (26), the amount of volatiles from the pre-heater or the electron treatment zone which are returned back into the flow prior to further electron beam treatment can be varied in a controllable manner to, in turn, vary the types of reactions taking place in the treatment zone.

As described herein, the method according to the present invention generally comprises the following steps:

1) A heavy oil feedstock is introduced to the process through Line #1. The flow rate is a function of the accelerator power and the capacity of the electron treatment zone. For an electron dose of 10 kGy supplied to the feedstock, throughput is up to 1.70 barrels per hour for every kilowatt of installed electron power.

2) The feedstock may be conditioned with air containing ozone produced by the electron/x-ray treatment of the cooling air stream. Ozone may also be added from other ozone-generating technologies. Any parts of the feedstock which are volatized during this preconditioning may be retained in the feedstock flow or may be vented off and returned to the feedstock flow just prior to subsequent electron treatment at Line #3.

3) The conditioned feedstock is pumped through Line #1 to the continuous flow preheater, where the feedstock is raised in temperature, up to a maximum of 425° C. Steam and preheated hydrogen donor gas, such as methane, may be injected into the feedstock either prior to the preheater or just prior to electron/x-ray treatment to control specific reactions. The light fractions released during preheating are pumped through Line #3 to either the Distillation Unit or recirculated back to the feedstock via Line #4 to enhance the effects of the cracking process.

4) The feedstock exits the preheater through Line #2 and enters the electron treatment Zone. As the temperature is maintained, the feedstock is treated with electrons or X-rays to a dose of up to 50 kGy. The treatment zone is operated at or near atmospheric pressure. The treatment zone is designed to insure that the feedstock depth during treatment is optimized for the electron or x-ray energy used. The flow rate, dictated by the required electron/x-ray dose, will be sufficient to minimize fouling within the apparatus. The process may include mixing the feedstock stream during electron treatment, either with baffles or blades in the flow path. The light fractions released during electron/x-ray treatment may be pumped through Line #5 to either the Distillation Unit or recirculated back to the feedstock stream prior to electron/x-ray treatment to further enhance the effects of the cracking process.

5) The accelerator produces either a pulsed or a continuous electron beam. The air stream from the electron/x-ray treatment zone with ozone produced during the electron/x-ray treatment, may be pumped to the inlet line for the feedstock (Line 7) to enhance the effects of the cracking process.

6) The accelerator facility may generate multiple beams, either with multiple accelerators or the use of beam splitters to allow the feedstock to be treated from multiple sides in the electron treatment zone. Standard shielding designs for accelerator facilities may be used for this facility.

7) The cracked feedstock is now appropriately conditioned and fed through Line #6 into the Distillation Unit. In the Distillation Unit, light fractions are volatilized and exit. The less volatile fraction of the feedstock stream exits the Distillation Unit and continues through the traditional heavy oil processing stages.

Since various modifications can be made in the invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense. 

1. A method of upgrading a heavy oil feedstock, the method comprising: forming a continuous flow of the heavy oil feedstock; heating the continuous flow to a prescribed temperature; cracking the heavy oil feedstock in the continuous flow by directing either electrons or x-rays at the continuous flow.
 2. The method according to claim 1 including recycling a separated portion comprising volatized parts of the continuous flow back into the continuous flow prior to electron cracking.
 3. The method according to claim 1 including varying constituents of the continuous flow subsequent to cracking by varying an amount of the separated portion recycled back into the continuous flow.
 4. The method according to claim 1 including recycling back into the flow a separated portion comprising a part of the continuous flow which is volatized when heating the flow to said prescribed temperature.
 5. The method according to claim 1 including preconditioning the continuous flow prior to heating to said prescribed temperature by adding to the flow a selected one or more of ozone, steam or a hydrogen donor gas and recycling back into the flow a separated portion comprising parts of the continuous flow which are volatized when preconditioning.
 6. The method according to claim 1 including reducing a cross sectional dimension of the continuous flow in one direction prior to electron cracking.
 7. The method according to claim 1 including recycling back into the flow a separated portion of the continuous flow comprising hydrocarbon molecules.
 8. The method according to claim 1 including electron or x-ray cracking at conditions near atmospheric pressure.
 9. The method according to claim 1 including mixing the continuous flow during electron or x-ray cracking.
 10. The method according to claim 1 including directing electrons at the continuous flow from more than one direction.
 11. A method according to claim 1 including arranging a portion of the continuous flow to comprise hydrocarbons having a boiling point lower than said prescribed temperature prior to electron or x-ray cracking by maintaining under pressure in the continuous flow at least a portion of hydrocarbons volatized during heating. 